The overall aim of the U.S. Principal Investigator's NIH Grant AI 37139 is to investigate the role of lipoarabinomanan (LAM) in the virulence and pathogenesis of tuberculosis and leprosy. Identification of truncated structural variants of LAM in ethambutol drug-resistant strains of mycobacteria has provided the PI with model compounds for both structural and functional studies aimed at defining the relevance of LAM in host-mycobacterial interactions. The present AIDS-FIRCA proposal is to investigate the structural features of LAM from clinical and laboratory strains of M. avium complex (MAC) that differ in colony morphology and drug resistance. Specifically, the proposal will address relationship of colony morphotypes, virulence and drug reasistance by defining the chemical nature of LAM from MAC, by examinig the effect of ethambutol on the arabinan biosynthesis in the cell wall of MAC, and by studying the biochemical markers that distinguish virulent and avirulent isolates.